Although it was discovered in 1879, for much of its history, scandium has been a commercially insignificant metal with few practical uses. More recently, however, scandia-stabilized zirconia has gained importance as a high efficiency electrolyte in solid oxide fuel cells, while high-intensity discharge (HID) lamps use scandium iodide for sports stadium and arena lighting to provide daytime-like color for television. Scandium alloys, and especially scandium aluminum alloys, have also attracted interest in various aerospace applications, as demonstrated by their use in the MiG-21 and MiG-29 aircraft.
Scandium alloys offer numerous advantages over other metal alloys in various applications. For example, some scandium-reinforced alloys are much stronger than their non-scandium counterparts. Moreover, the use of scandium in some metal alloys significantly improves the grain refinement of the alloys, and eliminates hot cracking and improves strength in welds. Scandium alloys also exhibit good resistance to corrosion.
Scandium-aluminum alloys are of particular commercial interest, since these alloys exhibit a lower specific gravity compared to the more widely used titanium aluminum alloys. Thus, for example, Sc—Al has a specific gravity of 2.8 compared to 4.5 for Ti6Al4V. In a commercial airline fleet, this difference in specific gravity translates into substantial fuel savings on an annual basis.
Despite the many advantages offered by scandium and its alloys, the widespread use of scandium has been hampered by the low availability (and consequently high cost) of the metal. Although scandium is not a particularly rare metal in terms of its abundance in the Earth's crust, there are currently no known, easily extractable deposits of minerals which contain high concentrations of the metal. Consequently, most scandium today is obtained as a byproduct of other metal recovery processes, typically from the treatment of tailings or metal sludges obtained from the refining of other metals. For example, scandium is frequently recovered as a byproduct of the treatment of tungsten and uranium tailings, or from waste streams resulting from the processing of titanium-containing ores and concentrates into titanium dioxide pigments. Scandium can also be obtained from the treatment of red mud, a waste product of the Bayer process used to refine bauxite into alumina.